There is enormous potential for oligonucleotides (ON) as therapeutics, but the challenge remains how to effectively deliver ON into cells. Cell membranes resist the cellular uptake of currently used charged ON. The application of various delivery systems has only partially solved the problem and is often associated with therapeutically unacceptable side effects. Low level cellular uptake has been the main reason of the failure of large number of ON targeting cancer, genetic-, and microorganism-mediated diseases. Specific aims for the Phase I were 1) development and validation of two new types of phosphoramidite monomers, 2) their use for the synthesis of ZATA ON with enhanced cellular uptake, and 3) demonstration that ZATA ON possess an optimal combination of properties necessary for high in vivo therapeutic activity, such as enhanced cell penetration, high efficacy toward silencing of target genes, low or lack of toxicity at therapeutic concentrations, maintenance of natural hybridization properties, stability in plasma/biological fluids, solubility n aqueous media and robust method of synthesis allowing scale-up. As demonstrated in the Progress Report section, we fully completed all Phase I specific tasks and, for the first time, have developed ON with new composition of matter that practically satisfies the complex criteria outlined herein. Particularly, novelties implemented in ZATA ON enabled a) 4 times higher cellular uptake vs. similar oligonucleotides without ZATA modifications, b) over 95% inhibition of cancer cell growth in culture with single treatment at a concentration as low as 1 M, c) high stability in serum, and d) lack of cytotoxicity at a concentration as high as 10 M. Our achievements can briefly be defined as a novel class of ON synthesized via standard phosphoramidite chemistry which permits facile attachment of Charge Neutralizing Groups (CNG) bearing positive charges at their termini capable of reaching the adjacent negative charges and neutralizing them. Charge-neutralization in combination with added partial hydrophobicity across the backbone of ON dramatically enhance cellular uptake and gene silencing efficacy. Our major goal for the Phase II of this technology development is further validation of ZATA ON by demonstrating their high therapeutic efficacy in vitro and in vivo (mouse) models. The main tasks for Phase II study are: 1) Optimization and scale-up of the synthesis of all four 2?-modified RNA phosphoramidites enabling the incorporation of optimal CNG (i.e. 1,3-Bis(2-(dimethylamino) ethoxy)propan-2-ol) into the backbones of our ON; 2) Synthesis and screening of over two dozen ON targeting oncogenic miR10b and miR21 in human glioblastoma and breast cancer cell lines; 3) Scale-up of the best ON drug candidate(s) and testing in vivo in mouse model using human glioblastoma xenografts as a target. Novelties developed in the Phase I study are subject to ZATA's new PCT patent application.